退火工艺对搅拌摩擦加工镁合金微观组织和显微硬度的影响

采用搅拌摩擦加工(Friction stir processing,FSP)技术对AZ31镁合金进行加工,通过采取不同温度及保温时间的退火工艺,研究了FSP镁合金在退火过程中的微观组织演变过程及硬度变化规律。结果表明,FSP成功制备了细晶AZ31镁合金,其平均晶粒尺寸细化程度达54.9%。当退火温度在200～300 ℃时,加工区(SZ)晶粒尺寸较为稳定,且组织发生不同程度的均匀化和细化;当温度超过300 ℃时,加工区晶粒互相吞噬而快速长大。在退火温度较低、短时间保温时热影响区(HAZ)组织变化不明显,而延长保温时间或者升高温度,HAZ区组织会迅速细化、均匀化;当退火温度超过300 ℃时,再结晶会在短时间内完成,随后晶粒继续长大。在300 ℃下保温60 min为最优退火工艺,可使SZ、HAZ组织分别细化10.9%、35.6%。

Effect of annealing process on microstructure and microhardness of magnesium alloy fabricated by friction stir processing

Friction stir processing (FSP) technology was adopted to prepare AZ31 magnesium alloy. The microstructure evolution and microhardness of the FSP magnesium alloy during annealing was studied by varying annealing temperature and preserving time. The results show that the fine grained AZ31 magnesium alloy are successfully prepared by FSP, and the average grain size is refined by 54.9%. When the annealing temperature is between 200-300 ℃, the average grain size in the stirring zone (SZ) is rather stable, and the structure is homogenized and refined in different degrees. When the annealing temperature is higher than 300 ℃, in the SZ the grains grow rapidly by consuming each other. In the heat affected zone (HAZ), when the annealing temperature is low, the microstructural evolution is insignificant after short-time preservation, while long time preserving and high temperature makes the microstructure in the HAZ to be refined and homogenized rapidly. When the annealing temperature exceeds 300 ℃, the recrystallization will be completed in a short time, then the grains in the HAZ begin to grow again. Annealing at 300 ℃ for 60 min is the optimum annealing process, after which the microstructure in the SZ and the HAZ can be refined by 10.9% and 35.6%, respectively.